Glacier melt threatens West Antarctic ice sheet

A new study has revealed that a major glacier in Antarctica could collapse because of warmer seas caused by climate change. Even worse, the glacial melt could destabilise the West Antarctic ice sheet — a 3 kilometre thick block of ice the size of Texas.

The research team, led by the University of Oxford’s Richard Katz , concluded the Pine Island glacier is most likely past its tipping point. It could lose half its ice in a century. This alone would add about 24 centimetres to world sea levels.

The nearby Thwaites glacier is also thinning rapidly. The melting of the two glaciers combined could raise sea levels by half a metre or more.

Past studies relied on satellite measurements to show the Pine Island’s glacier’s ice flow was about 25% faster than 30 years before. The January 13 New Scientist said Katz’s study of the glacier was the first to model changes in three dimensions.

The team found warmer water has found its way underneath the glacier’s “grounding line” — the point where the ice meets the ocean floor — melting it from below.

The model suggested the warm water has encroached far enough to mean the glacier has passed the point of no return. The rate of melting is predicted to rapidly increase. However, the team also warned that their model is probably over-optimistic and the glaciers could vanish even faster that projected, said New Scientist.

The Pine Island and Thwaites glaciers drain about 20% of the huge West Antarctic ice sheet. The collapse of the glaciers could cause the ice sheet to change rapidly.

Katz told ScienceDaily.com that if the ice sheet’s grounding line is pushed back too far the consequences could be dramatic: “Our model shows how instability in the grounding line, caused by gradual climatic changes, has the potential to reach a ‘tipping point’ where disintegration of the [West Antarctic] ice sheet could occur.”

In his 2009 book Storms of my Grandchildren, NASA climate scientist James Hansen said loss of the entire West Antarctic ice sheet could lead to sea-level rises of 6-7 metres.

“The West Antarctic ice sheet is especially vulnerable to removal of its ice shelves, because much of that ice sheet rests on bedrock several hundred metres below sea level.”

Hansen said preventing the loss of the ice sheet is of great importance.

“Once the ice sheets’ collapse begins, global coastal devastations and their economic reverberations may make it impractical for humanity to take actions to rapidly reverse climate forcings. Thus if we trigger the collapse of the West Antarctic ice sheet, sea level rise may continue to even much higher levels via contributions from the Greenland and East Antarctica ice sheets.”

Estimates of ice sheet loss in Antarctica were absent from the 2007 Intergovernmental Panel on Climate Change (IPCC) report. Instead, the report assumed the climate change would not affect the Antarctic. As a result, the IPCC’s median prediction for sea-level rise by mid-century was only 44 centimetres.

In a recent article on Geology.com, the University of Texas’ Marc Airhart said, “the IPCC’s restrained estimate about the ice flow, and its possible contribution to sea level rise, was not, however, a heartening sign. Rather, it reflected the consensus view that changes in the Antarctic have been so rapid, science can not yet account for them.”

However, a group of 26 climate scientists issued a report in December to update the outdated science in the IPCC report. In The Copenhagen Diagnosis the scientists said world sea-level rises has been “about 80% higher than IPCC projections from 2001.”

“Accounting for ice-sheets and glaciers, global sea-level rise may exceed 1 meter by 2100, with a rise of up to 2 meters considered an upper limit by this time. This is much higher than previously projected by the IPCC.”

One of the report’s authors, Professor Tim Lenton from the University of East Anglia said: “Climate change is accelerating towards the tipping points for polar ice sheets. That’s why we’re now projecting future sea level rise in metres rather than centimeters.”

The scientists concluded, “global emissions must peak then decline rapidly within the next five to ten years for the world to have a reasonable chance of avoiding the very worst impacts of climate change”.